AC (Alternating Current) grids have been used for a long time for power transmission. In more recent years, there is an increase in interest for DC (Direct Current) links, and in particular HVDC (High Voltage Direct Current) for power transmission. These DC links can be connected in DC grids with increasing complexity.
Typically, a DC grid is connected with the AC grid. However, such interconnection increases control complexity and may result in unpredictable and possibly undesired behaviour, e.g. after faults on transmission lines or nodes in the resulting transmission system.